A Virtual Private Network (VPN) is defined as a network in which customer connectivity amongst multiple sites is deployed on a shared infrastructure with the same access or security polices as a private network. Initial computers network were implemented with two major technologies: leased lines for permanent connectivity and dial-up lines for occasional connectivity requirements. With the introduction of new technologies in the service provider networks and new customer requirements, the VPN concept became more and more complex Introduction of new technology, called MPLS/YPN results in simpler customer routing and somewhat simpler service provider provisioning and makes possible a number of topologies that are hard to implement in either the overlay or peer-to-peer model.
